If California grid planners are worried about the famous “Duck Curve,” representing the future disruptions that distributed solar PV systems will have on the state’s grid, they should check out Hawaii’s “Nessie Curve.”

That’s the term that Hawaii’s utility and grid planners have adopted for the real-world grid disruptions they’re seeing today from the island state’s growing solar PV generation mix. They’ve dubbed it the Nessie Curve after the nickname for the mythic Scottish lake-dwelling dinosaur, the Loch Ness Monster.

Unlike California’s Duck Curve, Hawaii’s curve is happening today, not in the future. Also, unlike California’s projection of reduced, but not erased, demand due to solar PV generation, Hawaii’s curve actually drops “underwater” during peak solar times of the day.

In other words, Hawaii is already seeing enough solar coming onto parts of its grid to start feeding back power onto certain distribution circuits on sunny days, and to drive system-wide demand curves below zero on certain peak days.

This graph is from a presentation made by Dora Nakafuji, director of renewable energy planning for Hawaii Electric Co. (HECO), at last month’s DistribuTECH conference in San Antonio, Texas. This chart represents typical circuits on the island of Oahu, where lucrative incentives have led to a huge increase in distributed solar PV. As of the most recent tally, 10 percent of the island’s customers have rooftop PV, which equates to 29,558 systems with a cumulative nameplate generating capacity of 221 megawatts.

“It’s starting to look like this Loch Ness Monster,” Nakafuji said, pointing to the mid-day sag in residential energy demand, as rooftop solar PV energy supply exceeds the energy demand on those circuits, then the steep curve upward as solar fades away and late afternoon demand increases.

That’s made Hawaii a vanguard in testing the boundaries of how to manage such large penetrations of customer-owned generation, which is outside the utility’s control, and largely unmonitored by utilities and grid operators to manage the balance of energy supply and demand. In a controversial move, HECO has put new interconnection requirements in place for even small-scale rooftop solar PV systems, which has slammed the brakes on new projects and drawn the ire of the solar industry.

As Nakafuji pointed out, one of the clearest representations of this disruption can be seen in the data that tracks daily demand from homes, businesses and other energy users on distribution circuits. Because distributed solar PV causes that demand to drop during sunny mid-afternoon hours and then fades away in late afternoon and evening, it’s giving HECO a much more challenging situation in terms of turning down its oil-fired generators when solar is at its peak, then ramping them up much faster than it’s used to when solar power availability declines.

The radical effect that distributed solar has had on Hawaii’s load curve is demonstrated by the following graph, tracking changes from 2010 to 2013 on average 46kV transformer loading. On one peak day in August, the system experienced a backfeed condition, not just on some individual circuits, but across the system as a whole, she noted.

That’s the same challenge that California grid operators believe may start occurring on that state’s much larger and more integrated grid in coming years, as represented by the well-known “Duck Curve” from California Independent System Operator (CAISO). But while California is facing this effect in the future, Hawaii it facing it today -- and it’s doing so with an island system with far fewer generation resources to tap to manage it.

This becomes a serious problem for managing the addition of new solar systems on heavily impacted circuits, Nakafuji noted. “We’ve noticed that 16 percent of the customers on the feeders who have the PV are already pushing the daytime minimum load up to over 100 percent. That means it’s back-feeding on our system. That becomes a concern,” she said, because circuits that send power back up to distribution transformers and substations cause all sorts of technical and operational challenges, with attendant costs.

Even getting the data to understand what’s happening on Hawaii’s grid has been a challenge, Nakafuji noted. “One of the things about renewable integration is, we really need locational data,” she said. As this map of Oahu’s distribution circuits indicates, certain parts of the island are far more affected by solar PV penetration than others.

“We’ve been deploying sensors out in the field to correlate” information pulled in from existing SCADA systems, she said, since “this was information the traditional system didn’t look at.” HECO is also planning to deploy smart meters, which could add more data to help guide day-to-day grid management decisions, she said.

Then there’s the essential problem of relying on a solar PV fleet for the island’s energy needs, she said -- “What do we do when those renewables aren’t there?” HECO is investing lots of money in weather forecasting systems and distributed energy analysis and management technology, as part of a program funded by the Department of Energy's SunShot grant initiative (PDF).

Jeff St. John is a reporter and analyst covering the green technology space, with a particular focus on smart grid, smart buildings, energy efficiency, demand response, energy storage, green IT, renewable energy and technology to integrate distributed, intermittent green energy into the grid. Jeff majored in English and graduated from the University of California at Berkeley in 1994. He ...

I don't know how much Hawaian infrastructure and real estate is at risk from rising sea levels but I would think they would be very concerned about CO2 - enough to push the limit on grid PV by investing in better distribution and accepting substantial hybrid diesel that would include batteries,super capacitors,etc. for quick response to variable generation. They mite accept nuclear generation but not politically likely. The only other option I see is some of the floating off shore wind that is being piloted now.

German scenario studies indicate no problem with up to 40-50% of all electricity produced with renewable.With now ~24% of all consumed electricity produced by renewable, their grid has superior reliability: Average customer connection has a total outage time of ~15min/year.

That reliability increased from 30min./year down ~8years ago, towards 15min/year down now, when the share of wind+solar became substantial. Main reasons more distributed generation by thousands of small units. So a sudden outage of a 1MW wind turbine of a 10KW solar installation does not affect the grid much, which is totally different with a break down of a 900MW plant.

Pity that the German grid regulator has come out several times then saying that the grid is becoming less stable and that specifcially due to renewable surges, more interventions were required to keep the grid stable.

Further stop conflating Germany renewables with solar, the thrust of the article here. Around 45% of German renewable electricity is in the form of biomass and hydro. ~60% of renewable energy is biomass. The total investment for biomass was estimated at around 2.5 billion. Solar providing 8% of the total renewable energy share has cost over 11 billion in investments according the AGEE stat. What to make of this? Any comment thus on which is the better valued technology (PS the subsidy case is worse for solar again)?

35,000 MW x a ten-yr average of about $5,000,000/MW = $175 billion just for installing the PV systems and connecting them to the grid. Add to that grid modifications and increased wear and tearr of increased part-load operation of OTHER generators, and the costs are well over $200 billion.

Then look into the expansion plans (e.g. VDE or Agora). Nearly only solar+wind.Not strange as the Germans want to keep their forests, etc.

"...German grid regulator has come out several times then saying that the grid is becoming less stable and that specifcially due to renewable surges..."Of course. They want to minimize further delay with the grid upgrades, so they put political pressure up. And they succeeded as last summer German parliament installed a special law in order to minimize delays due to NIMBY etc.

Important as those delays caused that the FiT's are adapted such that the max. installation rate of wind+solar is ~5-6GW/year now. So they are sure to keep their excellent grid reliability. With the grid upgrades they can increase the installation rate.

These grid stability remarks are published in English by Bloomberg etc. totally out of their connection. Apperently in order to rise fear or so (may be in order to prevent USA follows Germany). How important is it?In the Netherlands it got no attention at all. Stronger. We are installing two new high power interconnections with the German grid, so we can import more of their cheap, reliable electricity.We will sell part of it to UK, as in UK wholesale prices are even higher than in Netherlands.

Nathan, Hawaii is already quite experienced with how batteries can help them on their road to solartopia. They have very real experience with the high cost of having thousands of costly batteries burn to ashes within months of being commissioned, while emitting toxic fumes into the environment and putting hesitant firefighters at risk.

It could be a 3600 rpm, synchronous-converter system, as is used by GMP for its Lowell Mountain wind turbine facility.

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Voltage Regulating Facility: Lowell wind energy varies with the cube of the wind speed; double the wind speed, eight times the energy. According to ISO-NE, because the variations of the wind energy voltage are too excessive for the NEK grid, a 27.5 MVAR voltage regulating facility needs to be installed by GMP. It will be located adjacent to the Jay Peak 46 kV Switching Station, housed in a 40’ x 68’ x 45’5” tall building, surrounded by 70’ x 90’ x 8’ tall fencing.

The voltage regulating is performed by a Hyundai-supplied, 62-ton, synchronous-condenser system, operating at 3,600 rpm and at no load, 24/7/365 (high-speed idling, year-round), plus electrical systems to modify the variable wind energy by adding or subtracting reactive energy to satisfy below-criteria voltages on the 115 kV transmission system.

It requires an 800-hp motor to get it up to speed and maintain it there. The system will cost about $10.5 million and be operational by the Spring of 2014. During all of 2013 and part of 2014, Lowell will be operated in curtailed mode, as required by ISO-NE.

S-C systems have energy losses of about 3%, i.e., 97% efficient, plus the facility has its own levelized (Owning + O&M) costs, which will adversely affect the project economics. Energy loss of only the S-C system = 800 hp x .746 kW/hp x 8,760 hr/yr x 0.03 = 156,839 kWh/yr; that energy is subtracted from the energy fed to the grid.

http://psb.vermont.gov/sites/psb/files/248j/2013/02.%20Petition.pdf

*Newly-developed systems are available from GE, Siemens, Vestas, that perform two functions: vary the pitch of the blades, based on wind velocity, as measured at the nacelle, to more-efficiently obtain energy from the wind, and, using partially-charged batteries that absorb and supply energy, to reduce voltages variations. The resulting processed outputs are collected from each IWT and fed, via a substation, into the grid. The likely net effect, claimed by Vendors, is an increased CF and less disturbance of the grid.

Capital Cost: GMP calculated the Lowell capital cost at about $160 million, plus about $10.5 million for a synchronous-condenser system, per ISO-NE requirements, to minimize voltage variations and instabilities of the Northeast Kingdom grid, for a total of about $170.5 million.

The above capital costs may not include transmission upgrades ($10,280,000) and substation upgrades ($3,160,000 or $17,420,000) of which Vermont Electric Cooperative will pay 41% and GMP 59%. See page 14 of URL.

In other words: it's a big flywheel. Flywheel are great for many things except bulk energy storage. It is storage that the Hawaiian's need.

I wonder if they are contemplating deep ocean compressed air storage (pumping air into deep undersea balloons as a means of storing energy) like some of the carribean island nations are doing, or so I've heard. Such systems can store lots of energy and are supposed to be cheaper than batteries, but they are not cheap and also not efficient. eff= 50% or so?